1. Field of the Invention
This invention relates to a drivably connecting construction in a measuring instrument, for connecting a main body of a measuring instrument (slider) to a nut member threadably coupled to a feed screwshaft mainly used in a feeding mechanism of a high precision measuring instrument, such as a coordinate measuring instrument.
2. Description of the Prior Art
In general, a basic construction shown in FIG. 1 is adopted in the case of using a feed screwshaft in a feeding mechanism of a measuring instrument. More specifically, as shown in this drawing, a feed screwshaft 1 is rotated by a driving motor 2, a nut member 3 is threadably coupled onto the feed screwshaft 1, a main body 4 (slider) of the measuring instrument is connected to this nut member 3 and the main body 4 is moved commensurate to a rotation value of the feed screwshaft 1, being guided by a guide rail 5 extending in parallel to the feed screwshaft 1 and so on.
Now, when the nut member 3 and the main body 4 are integrally connected to each other in a manner not to be displaceable relative to each other, an excessively strong force applied to a particularly weak constituent may possibly cause the constituent to be damaged. Such errors may occur in the assembling accuracy wherein an error in exists between the feed screwshaft 1 and the guide rail 5, and where fluctuations (yawing, rolling and pitching) and the like occur during the rotation of the screwshaft.
To obviate the above-described disadvantages, there is known such an arrangement that the nut member 3 and the main body 4 of the measuring instrument are connected to each other through a resilient member, or a cylindrical portion is provided on the main body 4, and a ball coupled into this cylindrical portion is fixed to the nut member 3, whereby a relative displacement between the nut member 3 and the main body 4 is absorbed. However, the conventional device as described above is constructed only on the basis of the absorption of the relative displacement (shift in position) between the nut member 3 and the main body 4, and, when the conventional device is applied to a high precision and large-sized, as the case may be, measuring instrument such for example as a coordinate measuring instrument, an adverse influence on the measuring accuracy is disadvantageous, in particular.
More specifically, a tolerance capable of absorbing a relative displacement value between the nut member 3 and the main body 4 is high, whereas, for example, an error tends to occur easily in the feed value of the main body 4 due to a change in the sliding resistance with the guide rail 5 and the like, whereby it is difficult to maintain the proof accuracy of the feed value. In other words, with the conventional device, it has been permitted that the nut member 3 and the main body 4 may be shifted in the positional relationship with each other in each of the tridimensional directions, whereby it has been impossible to control the feed value with high accuracy, with the result that it has been impossible to carry out a high precision screw feed.